Multicolor dye developer diffusion transfer processes with pyrazolo-{8 3,4d{9 {0 pyrimidines

ABSTRACT

This application is concerned with the use of pyrazolo(3,4d)pyrimidines in dye developer diffusion transfer processes.

United States Patent 1 3,899,331

Bloom et al. Aug. 12, 1975 [54] MULTICOLOR DYE DEVELOPER 3,265,498 8/1966 Rogers et al 96/3 DIFFUSION TRANSFER PROCESSES WITH lsogers rang PYRAZOLO'[34D] PYRIMIDINES 3,785,814 1/1974 Land et al 96/109 [75] Inventors: Stanley M. Bloom, Waban; Nicholas fladlekyfiakidesa Arlington, FOREIGN PATENTS OR APPLICATIONS of a 701,054 12/1953 United Kingdom 96/109 [73] Assignee: Polaroid Corporation, Cambridge, 716,327 10/1954 United Kingdom 96/ 109 Mass.

[22] Filed: 1973 Primary ExaminerNOrman G. Torchin 21] A l 415 7 3 Assistant ExaminerRichard L. Schilling Attorney, Agent, or Firm-Stanley H. Mervis [52] US. Cl 96/3; 93/663 UX; 96/66.5 UX; 96/77; 96/95 UX; 96/109 UX [51] Int. Cl. G03c 7/00; G03c 5/30; G030 1/40; [57] ABSTRACT G030 l/06; G030 1/48; G030 l/34 of Search 95, R, application is concerned the use of pyraz0lo 96/3, 77 [3,4d]pyrimidines in dye developer diffusion transfer processes. [56] References Cited UNITED STATES PATENTS 19 Claims, 2 Drawing Figures 3,260,597 7/1966 Weyerts et al 96/3 30 28 26 2.4 2.2 2.0 L8 1.6 1.4 1.2 L0 .8 .6 4 .2 O

LOG E MULTICOLOR DYE DEVELOPER DIFFUSION TRANSFER PROCESSES WITH PYRAZOLO-[3,4D] PYRIMIDINES This invention is concerned with color photography and, more particularly, with photographic processes which provide dye developer diffusion transfer color images.

US. Pat. No. 2,983,606 issued May 9, 1961 to Howard G. Rogers, and numerous other patents disclose photographic processes employing dye developers and, in particular, the formation of diffusion transfer color images by the use of dye developers.

vThe present invention is concerned with the use of pyrazolo-[3,4d]pyrimidines, and particularly 4- aminopyrazolo-[3,4dlpyrimidines, in such dye developer photographic processes.

The primary object of thisinvention is to provide novel photographic processes wherein an exposed silver halide emulsion is developed in the presence of a dye developer and a pyrazolo-[3,4d]pyrimidine.

A further object of this invention is to provide novel multicolor dye developer diffusion transfer processes wherein the red, green or blue H and D curve may be preferentially shifted by performing said process in the presence of a pyrazolo-[3,4d]pyrimidine.

Other objects of this invention will in part be obvious and will in part appear hereinafter.

The invention accordingly comprises the product possessing the features, properties and the relation of components and the process involving the several steps and the relation and order of one or more of such steps with respect to each of the others which are exemplified in the following detailed disclosure, and the scope of the application of which will be indicated in the claims.

For a fuller understanding of the nature and objects of the invention. reference should be had to the following detailed description taken in conjunction with the accompanying drawings wherein:

FIG. 1 reproduces the characteristic curves of the red, green and blue densities of the neutral column of a multicolor transfer image obtained in accordance with one embodiment of this invention; and

FIG. 2 reproduces the characteristic curves of the red, green and blue densities of the neutral column of a multicolor transfer image obtained in a control experiment and reproduced for comparison purposes.

This invention is particularly directed to photographic processes wherein the desired color transfer image is a multicolor image obtained by processing an exposed multicolor photosensitive silver halide element with a processing composition distributed between two sheet-like elements, one of said elements including an image-receiving layer. The processing composition is so applied and confined within and between the two sheet-like elements as not to contact or wet outer surfaces of the superposed elements, thus providing a film unit or film packet whose external surfaces are dry. The processing composition, which may be viscous or nonviscous. preferably is distributed in viscous form from a single-use rupturable container; such pressure rupturable processing containers are frequently referred to as pods."

Multicolor diffusion transfer images may be obtained using dye developers by several techniques. A particularly useful technique employs an integral multilayer photosensitive element, such as is disclosed in the aforementioned US. Pat. No. 2,983,606, and particularly with reference to FIG. 9 thereof, and also in U.S. Pat. No. 3,345,163 issued Oct. 3, 1967 to Edwin H. Land and Howard G. Rogers,wherein at least two selectively sensitized photosensitive strata, superposed on a common support, are processed, simultaneously and without separation, with a single (common) imagereceiving layer. A suitable arrangement of this type for obtaining multicolor images utilizing subtractive color principles comprises a support carrying a red-sensitive silver halide emulsion stratum, a green-sensitive silver halide emulsion stratum and a blue-sensitive silver halide emulsion stratum, said emulsions having associated therewith, respectively, a cyan dye developer, a magenta dye developer and a yellow dye developer. The dye developer may be positioned in the silver halide emulsion stratum, for example in the form of particles, or it may be disposed in a stratum behind the appropriate silver halide emulsion stratum with respect to the exposing light. Each set of silver halide emulsion and associated dye developer strata may be separated from other sets by suitable interlaycrs, for example, by a layer or stratum of gelatin, polyvinyl alcohol, or other polymeric materials known in the art. In certain instances, it may be desirable to incorporate a yellow filter in front of the green-sensitive emulsion to avoid improper exposure of said emulsion, by blue light, and such a yellow filter may be incorporated in the appropriately positioned interlayer. However, such a separate yellow filter may be omitted where a yellow dye developer of the appropriate spectral characteristics is present in a quantity and state capable of functioning as the requisite yellow filter. Procedures and suitable components for preparing such integral multicolor photosensitive elements are described in numerous patents and are well known in the art.

Following photoexposure, the photosensitive element is processed by application of a processing composition, for example, by immersion, coating, spraying, flowing, etc., in the dark. The exposed photosensitive element may be superposed prior to, during, or after application of the processing composition on a sheetlike element which may include an image-receiving layer. In one commercial embodiment, the processing composition is applied to the photosensitive element in a substantially uniform layer as the photosensitive element is brought into superposed relationship with the image-receiving layer. The liquid processing composition permeates the layers of the photosensitive element to initiate and effect development of the latent images contained therein. The dye developers are immobilized or precipitated imagewise in developed areas as a consequence of and in proportion to the silver halide development. This immobilization is. at least in part, due

to a change. in the solubility characteristics of the dye developers upon oxidation and especially as regards its solubility in alkaline solution. In undeveloped and partially developed areas of the silver halide emulsion layers, the respective unoxidized (unreacted) dye developers are diffusible. Development thus provides an imagewise distribution of unoxidized dye developer, diffusible in the alkaline processing composition, as a function of the point-to-point degree of exposure of a silver halide emulsion layer. At least part of each of these imagewise distributions of unoxidized dye developer is transferred, by imbibition. to a superposed image-receiving layer, said transfer substantially excluding oxidized dye developer. The image-receiving layer receives a depthwise diffusion; from'each developed silver halide emulsion, of uno'xi'dized dye developer without appreciably disturbing the imagewise distribution thereof to provide a reversed or positive color image of each developed silver image. The imagereceiving layer may contain a mordant and/or other agent to immobilize the dye' developer transferred thereto. lf the color of a transferred dye developer is affected by changes in the pH of the image-receiving layer, this pH may be adjusted in accordance with wellknown techniques to provide a pH affording the desired color. 'In the preferred embodiments of said U.S. Pat. No. 2,983,606 and in certain commercial applicationsthereof, the desired positive multicolor image is viewed by separating the image-receiving layer from the photosensitive element at the end of a suitable imbibition period.

In a more recent commercial application of the dye developer process, the image-receiving layer is not separated from its superposed relationship with the photosensitive layers subsequent to transfer image formation. Instead, the color image in the image-receiving layer is viewed through a transparent support. The aforementioned U.S. Pat. No. 2,983,606 discloses such an embodiment, the processing composition including a white pigment, such as titanium dioxide, in a quantity effective to mask or hide from view the developed silver halide emulsions now positioned behind the image-receiving layer when the image-receiving layer is viewed through the transparent support.

U.S. Pat. No. 3,415,644 issued Dec. 10, 1968 in the name of Edwin H. Land, discloses and claims photographic product's'and processes wherein a photosensitive element'and an image-receiving element are maintained in fixed, superposed relationship prior to exposure, and this'relationship is maintained as a laminate after processing and transfer image formation. The multicolor transfer image is viewed through a transparent (support) sheet against a reflecting, i.e., white, background. Photoexposure is made through said transparent support-and the layers carried thereon, including the image-receiving layer, and application of the processing composition provides a layer of lightreflecting material to provide a white background. The light-reflecting material (referred to in said patent as an ,opacifying' agent) is preferably titanium dioxide but a number of other materials have been disclosed as useful. In addition to providing a masking layer so the transfer image may be viewedwithout interference by the images in the developed silver halide emulsions, the light-reflecting material also performs an opacifying function by reflecting ambient light passing through the image-receiving layer and its transparent support when the photoexposed film unit is removed from the camera before transfer image formation is completed, thereby acting to protect the photoexposed silver halide emulsions from post-exposure fogging by such light.

U.S. Pat. No. 3,647,437 issued Mar. 7, 1972 to Edwin H. Land is concerned with improvements in the above-mentioned processes, and discloses the provision of a light-absorbing material, sometimes referred to as an optical filter agent, to permit such processes to be performed outside of the camera in which photoexposure is effected and to be so-performed under much .more intense ambient light" conditions. The lightabsorbing material or optical filter agent, preferably a dye, is so positioned in the film unit and/or constituted as not to interfere with photoexposure (by absorbing light during photoexposure) but so positioned between the photoexposed silver halide emulsions and the transparent support during processing after photoexposure as to absorb light which otherwise might fog the photoexposed emulsions. Furthermore, the light-absorbing material is so constituted and/or positioned after processing as not to interfere with viewing the desired image in its proper colors shortly after said image has been formed. In the preferred embodiments, the optical filter agent is a dye and is initially contained in the processing composition together with a light-reflecting material, e.g., titanium dioxide. The concentration of this light-absorbing dye is selected to provide the light transmission opacity required to perform the particular process under the selected light conditions, and a plurality of such dyes selected to together provide absorption over the visible spectrum is utilized in multicolor embodiments.

in a particularly useful embodiment, the lightabsorbing dye is highly colored at the pH of the processing composition, e.g., 13-14, but is substantially non-absorbing of visible light at a lower pH, e.g., less than 10-12. This pH reduction may be effected by an acid-reacting reagent appropriately positioned in the film unit, e.g., in a layer between the transparent support and the image-receiving layer. Suitable acidreacting reagents, preferably polymeric acids, are disclosed in the aforementioned U.S. Pat. Nos. 3,415,644 and 3,647,437 to which reference may be made for more specific information.

Suitable materials for use as the image-receiving layer are disclosed in the aforementioned patents. Preferred image-receiving layers comprise polyvinyl alcohol or gelatin containing a dye mordant such as poly-4- vinylpyridine, as disclosed in U.S. Pat. No. 3,148,061, issued Sept. 8, 1964.

As disclosed in the previously cited patents, the liquid processing composition referred to for effecting multicolor diffusion transfer processes comprises at least an aqueous solution of an alkaline material, for example, sodium hydroxide, potassium hydroxide, and the like, and preferably possesses a pH in excess of 12, and most preferably includes a viscosity-increasing compound constituting a film-forming material of the type which, when the composition is spread and dried, forms a relatively firm and relatively stable film. Preferred film-forming materials comprise high molecular weight polymers such as polymeric, water-soluble ethers, for example, a hydroxyethyl cellulose or sodium carboxymethyl cellulose, which are substantially inert in alkaline solution. Other film-forming materials or thickening agents whose ability to increase viscosity is unimpaired if left in alkaline solution for extended periods of time also may be used. The film-forming material is preferably contained in the processing composition in such suitable quantities as to impart to the composition a viscosity appropriate for the particular method of application to be used, such viscosity being in excess of cps. at a temperature of approximately 24 C. and preferably in the order of 100,000 cps. to 200,000 cps. at that temperature.

Dye developers are well known in the art and are compounds which contain both a silver halide developing function and the chromophoric system of a dye. By

a silver halide developing function" is meant a grouping adapted to develop exposedsilver halide. The-dye developer as incorporated in the photosensitive element may have a latent silver halide developing function, i.e., the dye developer may contain a moiety which is a precursor of the silver halide developing function or moiety, the active functional group being formed in situ following application of the processing composition, e.g., by alkaline hydrolysis of an esterified hydroquinonyl group. A preferred silver halide devel oping function is a hydroquinonyl group. Other particularly useful developing functions include ,orthodihydroxyphenyl and orthoand para-amino substituted hydroxyphenyl groups. In general, the developing function includes a benzenoid silver halide developing function, that is, an aromatic silver halide developing group which forms quinonoidor quinone substances when oxidized. The dye developers usually are selected for their ability to provide colors -.useful in carrying out subtractive color photography, e.g., cyan, magenta and yellow. Other colors,-of course, may be provided to meet the needs of a particular system.

For convenience, the disclosures of the abovemen tioned US. Pat. Nos, 2,983,606, 3,415,644 and 3,647,437 are hereby incorporated herein, as is the-disclosure of the copending application of Edwin H. Land, Stanley M. Bloom and Howard G. Rogers, Ser. No. 246.669 filed Apr. 24, 1972 (now US. Pat. No. 3,801,318, issued Apr. 2, 1974). l

In such multicolor applications of diffusion transfer color processes, variations in manufacturing conditions may result in undesired variations in the sensitometric response. e.g., speed or contrast, of one silver halide emulsion relative to the sensitometric response of either or both of the other silver halide emulsions. Such undesired variations may be reflected in changes in the H and D curve of, e.g., the red record, relative to the H and D curves of the green and blue records, and may be manifested in the ultimate multicolor image as a shift in color balance, e.g., toward the red. The present invention is concerned with reducing or avoiding such effects by performing the process in the presence of a reagent effective to improve the sensitometric response of a multicolor photosensitive element which would exhibit such undesired effects if processed in the absence of said reagent.

In accordance with this invention, it has been found that multicolor dye developer transfer images having more desirable sensitometric properties may be obtained by processing an integral multilayer photosensitive element in the presence of a pyrazolo- [3,4d]pyrimidine of the formulaz wherein each y is hydrogen or a 1 to carbon alkyl group and X is hydrogen, NH or NHR, R being a l to 5 carbon alkyl or an aralkyl group of 7 to 10 carbons. As examples of suitable I pyrazolo- [3,4d]pyrimidins, mention may be made of pyrazolo- [3 4d] pyrimidine 4-benzy1amino-pyrazo lo- [3 ,4d] pyrimidine The number of carbons in the alkyl and/or aralkyl groups as stated are sufficiently small so that the pyrazolo-[ 3,4d]pyrimidine may be dissolved in an alkaline processing composition and diffuse into the photosensitive element at a useful rate. Larger or other substituents may also be present provided the pyrazolo- [3,4d]pyrimidine may be dissolved and diffuse at a desired rate during processing.

The pyrazolo-pyrimidine is initially positioned in the processing composition so that it is in solution when development is initiated. If a delay in the availability of some or all of the pyrazolo-l 3,4dlpyrimidine is desired, the appropriate quantity may be initially positioned in a layer of the film unit, the time required to dissolve and diffuse fromthat location to the silver halide providing the desired delay.

The pyrazolo-l3,4d]pyrimidines are known compounds and may be prepared by known procedures; see, for example, Robins, Journal of the American Chemical Society, Vol. 78, pp. 784-790 (1956).

It has been found that the pyrazolo- [3,4d]pyrimidines are effective to selectively shift the speeds of the individual silver halide emulsions of an integral multilayer dye developer photosensitive element, and that this selective speed shift may be effected as a function of the concentration of the pyrazolo- [3,4d]pyrimidine. Assuming a multilayer negative in which the silver halide emulsion layer closest to the image-receiving layer is blue-sensitive and the silver halide emulsion layer farthest from the image-receiving layer is red-sensitive, and the processing application first permeates the blue-sensitive silver halide emulsion layer, the red speed will be the first speed to be slowed down, followed by the green speed and finally the blue speed, as the concentration of the pyrazolo- [3,4d]pyrimidine is increased. The mechanism by which this suprising effect is achieved is not known. It has been found that the pyrazolo-pyrimidines are capable of acting as an antifoggant in dye developer processes, but they are weaker antifoggants than such a well known antifoggant as benzimidazole. Furthermore, the concentrations at which the pyrazolopyrimidines give useful antifoggant activity are much greater than the concentrations at which they have been found to effect a useful selective speed shift.

The pyrazolo-[3,4d]pyrimidines have been found to be most effective when used in combination with a 6- alkylamino purine of the formula:

wherein R is an alkyl group, it being understood that 25 alkyl" is intended to include aralkyl, such as 3 acm1-o s l C an- CH CH3 N=Y=C C N v H O -m-c'm e no l c11 cs f c on m4 s N:':-=C H i cs c11 I so -ua-cu on cn a uo-cn --CH 7 2 n-so B N C HO-CH -cu l R magenta: N20

Where the alkyl group is a simple alkyl group, better results are generally obtained when the alkyl group contains more than one or two carbons. As will be apparent from the above, the alkyl group may be substituted, e.g., by halogen, alkoxy, etc. The use of 6- alkylamino purines in dye developer processes is the subject of the copending application of Edwin H. Land, Stanley M. Bloom and Howard G. Rogers, Ser. No. 211,718 filed Dec. 23, 1972 (now US. Pat. No. 3,785,814, issued Jan. 15, 1974).

This invention will be further illustrated by the following examples intended to be illustrative only.

EXAMPLE 1 A multicolor photosensitive element using, as the cyan, magenta and yellow dye developers yellow:

was prepared by coating a gelatin-subcoated 4 mil opaque polyethyleneterephthalate film base with the following layers:

1. a layer of cyan dye developer dispersed in gelatin and coated at a coverage of about 54 mgs/ft. of dye and about 87 mgs./ft. of gelatin;

2. a red-sensitive gelatino silver iodochlorobromide emulsion coated at a coverage of about 140 mgsQ/ft. of silver and about 62 mgs./ft. of gelatin;

3. a layer of a 60-30-4-6 copolymer of butylacrylate, diacetone acrylamide, styrene and methacrylic acid and polyacrylamide coated at a coverage of about l75 mgs./ft. of the copolymer and about 5 mgs./ft. of polyacrylamide;

4. a layer of magenta dye developer dispersed in gelatin and coated at a coverage of about 75 mgs./ft. of dye and about 67 mgs./it. of gelatin;

5. a green-sensitive gelatino silver iodochlorobromide emulsion coated at a coverage of about 80 mgs./ft. of silver and about mgs./ft. of gelatin;

6. a layer containing the copolymer referred to above in layer 3 and polyacrylamide coated at a coverage of about 95 mgs./ft. of copolymer and about 12 mgs./ft. of polyacrylamide;

7. a layer of yellow dye developer dispersed in gelatin and coated at a coverage of about 83 mgs./ft. of dye and about 59 mgs./ft. of gelatin;

8. a blue-sensitive gelatino silver iodobromide emulsion layer including the auxiliary developer 4'- methylphenyl hydroquinone coated at a coverage of about 120 mgs./ft. of silver, about 80 mgs./ft. of gelatin and about 30 mgs./ft. of auxiliary developer; and

9. a layer of gelatin coated at a coverage of about mgsJft. of gelatin.

A transparent 4 mil polyethylene terephthalate film base was coated, in succession, with the following layers to form an image-receiving component:

1. as a polymeric acid layer, the partially butyl ester o o H ll C-CH2-CH2 of polyethylene/maleic anhydride copolymer at a coverage of about 2,500 mgs./ft.

2. a timing layer containing about a 40:1 ratio of a -30-4-6 copolymer of butylacrylate, diacetone acrylamide, styrene and methacrylic acid and polyacrylamide at a coverage of aboutSOO mgs./ft.- and 3. a polymeric image-receiving layer containing a 2:1 mixture, by weight, of polyvinyl alcohol and poly-4- vinylpyridine, at a coverage of about 300 mgsJft. two components thus prepared were then taped together to provide an integral film unit, with a rupturable container retaining an aqueous alkaline processing solution fixedly mounted on the leading edge of each of the components, by'pressure-sensitive tapes, so that, upon application of compressive pressure to the container to rupture the containers marginal seal, its contents would be distributed between the image-receiving layer and the gelatin overcoat layer of the photosensitive component. The aqueous alkaline processing composition comprised:

Potassium hydroxide 4.59 g. N-henzyl-a-picolinium bromide (50% solution in water) 1.25 g. N-phcnethyl-a-picolinium bromide 072 g. Sodium carboxymethyl cellulose (Hercules Type 7H4F providin'g a viscosity of 3,000 cps. at l71 in water at 25C.) 1.07 g. Titanium dioxide 4L8 g. fi-methyl uracil 0.29 g. bis-( B-aminoethyl )-sulfide 0.02 g. Lithium nitrate 0.97 g. Benzotriazole 0.56 g. 6-methyl-5-bromo-4- azabenzimidazole 0.28 g. Colloidal silica aqueous dispersion (30% SiO L82 g. N-2-hydroxyethyl-N.N'. N'-triscarboxymethyl-ethylcne diamine 0.82 g. 4-amino-pyrazolo-[3.4d1pyrimidine 0.3 g. Lithium hydroxide 0.2 g. -benzylamino-purine 0.39 g. Polyethylene glycol (molecular weight 6,000) 0.54 g.

SOC

Water to make 100 g.

The photosensitive element was exposed through the transparentsupport and the layers thereon, a layer approximately 0.0026 inch thick of the processing composition wasdistributed by passing the film unit be- ,tween a pair of pressure-applying rolls and into a lighted area. The resulting laminate was maintained intact to provide a multicolor integral negative-positive reflection print which exhibited good color quality and separation. The neutral density column of the multicolor transfer image exhibited the following reflection densities:

Red Green multicolor transfer image exhibited the following reflection densities:

Red Green Blue Dim. 1.98 2.1 2.01 0.12 (1.1 0.18

The characteristic curves of the red, green and blue densities of the neutral column of the control image are reproduced in FIG. 1.

A comparison of the characteristic curves reproduced in FIGS. 1 and 2 clearly shows that the addition of the 4-amino-pyrazolo-[3,4d]pyrimidine was effective in shifting the red H and D curve relative to the green and blue H and D curves.

The above illustrated ability of the pyrazolo- [3,4d]pyrimidines to preferentially shift the sensitometric response of one or more of the silver halide emulsions is particularly useful when employed in combination with the selective preexposure disclosed and claimed in the copending application of Edwin H. Land, Ser. No. 300,710 filed Oct. 25, 1972 (now U.S. Pat. No. 3,819,376, issued June 25, 1974).

EXAMPLE 2 A processing composition was prepared like that debenzylamino-purine were omitted, and the concentration of the 4-aminopyrazolo-[3,4d]pyrimidine was 1.0%. A good quality multicolor image was obtained. When the experiment was repeated omitting the 4- aminopyrazolo-[3,4d]pyrimidine, substantial fogging with resultant loss of transfer density was observed. This comparison demonstrates the ability of pyrazolo- [3,4d]pyrimidines to act as the only necessary antifoggant when used in concentrations greater than that effective simply to shift an H and D curve.

In general, it has been found that incorporation of a pyrazolo-[3,4d]pyrimidine in the processing composition in a concentration of about 0.1 to 0.7%, by weight, is effective to provide useful shifting of one or more of the H and D curves. The particular concentration most useful with a given photosensitive element and processing composition, of course, may be readily determined by routine testing.-

While the invention has been illustrated as applied to the formation of integral negative-positive multicolor reflection prints, it will be understood that the invention also may be employed in the preparation of other diffusion transfer dye developer images, including monochromatic, black and white, and multicolor transfer images which are separated from the photosensitive layers after image formation. The invention is also applicable to diffusion transfer processes providing integral negative-positive reflection prints wherein the light-reflecting layer is not provided by a pigment in the processing composition but is provided, e.g., by a preformed layer of titanium dioxide, and the imagereceiving layer is carried by the same support as the photosensitive layers, as taught in U.S. Pat. Nos. 3,594,164 and 3,594,165, both issued July 20, 1971 to Howard G. Rogers.

Development is advantageously effected in the presence of an onium compound, particularly a quaternary ammonium compound, in accordance with the processes disclosed in U.S. Pat. No. 3,173,786 issued Mar. 16, 1965 to Milton Green and Howard G. Rogers. Quaternary ammonium compounds which form an active methylene compound in alkali are especially useful.

Development may be effected in the presence of a colorless auxiliary or accelerating developing agent, such as a 3-pyrazolidone or a hydroquinone, such as 4'-methylphenylhydroquinone, which may be initially positioned in a layer of the photosensitive element or in the processing composition, in accordance with known techniques.

The imagereceiving element may be prepared according to the disclosure of U.S. Pat. No. 3,362,819 issued Jan. 9, 1968 to Edwin H. Land and U.S. Pat. No. 3,455,686 issued July 15, 1968 to Leonard C. Farney, Howard G. Rogers and Richard W. Young.

Since certain changes may be made in the above product and process without departing from the scope of the invention herein involved, it is intended that all matter contained in the above description shall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

l. A diffusion transfer color process comprising exposing a photosensitive element comprising a bluesensitive silver halide emulsion having a yellow dye developer associated therewith, a green-sensitive silver halide emulsion having a magenta dye developer associated therewith, and a red-sensitive silver halide emulsion having a cyan dye developer associated therewith, applying an aqueous alkaline processing composition to said exposed photosensitive element to effect development and to form an imagewise distribution of unoxidized dye developer in undeveloped areas of each of said silver halide emulsions as a function of said development, said process including the step of transferring by diffusion at least a portion of said imagewise distributions of unoxidized dye developer to an imagereceiving layer in superposed relationship therewith to thereby provide a multicolor diffusion transfer image, said development being effected in the presence of a pyrazolo-[3,4d]pyrimidine of the formula wherein each Y is hydrogen or a l to carbon alkyl group and X is hydrogen, NH or NH-R, R being a 1 to 5 carbon alkyl group or an aralkyl group of 7 to carbons.

2. A diffusion transfer color process as defined in claim 1 wherein said pyrazolo-[3,4d]pyrimidine is pyrazolo-[3,4d]pyrimidine.

3. A diffusion transfer color process as defined in claim 1 wherein said pyrazolo-[3,4d]pyrimidine is 4- aminopyrazolo-[ 3 ,4d]pyrimidine.

4. A diffusion transfer color process as defined in claim 1 wherein said pyrazolo-[3,4d]pyrimidine is 4- benzylamino-pyrazolo-[ 3 ,4d ]pyrimidine.

5. A diffusion transfer color process as defined in claim 1 wherein there is also present during development a 6-alkylamino purine of the formula:

wherein R is an alkyl group.

6. A diffusion transfer color process as defined in claim 5 wherein said 6-alkylamino purine is 6- benzylamino purine.

7. A diffusion transfer color process as defined in claim 1 wherein said pyrazolo-[ 3,4d]pyrimidine is present in said processing composition in a concentration of about 0.1 to about 1 percent by weight of said processing composition.

' wherein 8. A diffusion transfer color process as defined in claim 1 wherein said pyrazolo-[ 3,4dlpyrimidine is present in said processing composition in a concentration of about 0.] to about 0.7 percent by weight of said processing composition.

9. A diffusion transfer color process as defined in claim 1 wherein a layer containing titanium dioxide is positioned between said image-receiving layer and said silver halide emulsions whereby said transfer image may be viewed without separating said image-receiving layer from said silver halide emulsion.

10. A diffusion transfer color process as defined in claim 9 wherein said titanium dioxide is initially present in said processing composition.

11. A photographic product for use in forming a diffusion transfer image in color comprising a photosensitive element comprising a support carrying a bluesensitive silver halide emulsion having a yellow dye developer associated therewith, a green-sensitive silver halide emulsion having a magenta dye developer associated therewith, and a red-sensitive silver halide emulsion having a cyan dye developer associated therewith; a second, sheet-like element positioned in superposed or superposable relationship with said photosensitive element; an image-receiving layer positioned in one of said elements; a rupturable container releasably holding an aqueous alkaline processing composition adapted, when distributed between a pair of predetermined layers carried by said photosensitive element and said second element, to develop said silver halide emulsions and provide a diffusion transfer image in color on said image-receiving layer; said processing composition including a pyrazolo-[3,4d1pyrimidine of the formula wherein each Y is hydrogen or a l to 5 carbon alkyl group and X is hydrogen, NH or NH-R, R being a 1 to 5 carbon alkyl group or an aralkyl group of 7 to 10 carbons.

12. A photographic product as defined in claim 11 wherein said pyrazolo-[3,4d]pyrimidine is pyrazolo- [3,4d]pyrimidine.

13. A photographic product as defined in claim 11 wherein said pyrazolo-[3,4d]pyrimidine is 4- aminopyrazolo-l 3 ,4d pyrimidine.

14. A photographic product as defined in claim 11 said pyrazolo-[3,4d]pyrimidine is 4- ben'zylamino-l 3 ,4d pyrimidine.

15. A photographic product as defined in claim ll wherein said second element includes said imagereceiving layer carried by a transparent support, and said processing composition includes titanium dioxide.

16. A photographic product as defined in claim '11 wherein said pyrazolo-[3,4d]pyrimidine is present in said processing composition in a concentration of about 0.1 to about 1 percent by weight of said processing composition.

17. A photographic product as defined in claim 11 wherein said pyrazolo-[3,4d]pyrimidine is present in about 0.1 to about 0.7 percent by weight of said cessing composition.

said processing composition in a concentration of pro- 18. A photographic product as defined in claim 11 wherein said processing composition also includes a 6- alkylamino purine of the formula rine. 

1. A DIFFUSION TRANSFER PROCESS COMPRISING EXPOSING A PHOTOSENSITIVE ELEMENT COMPRISING A BLUE-SENSITIVE SILVER HALIDE EMULSION HAVING A YELLOW DYE DEVELOPER ASSOCIATED THEREWITH, A GREEN-SENSITIVE SILVER HALIDE EMULSION HAVING A MAGENTA DYE DEVELOPER ASSOCIATED THEREWITH, AND A RED-SENSITIVE SILVER HALIDE EMULSION HAVING A CYAN DYE DEVELOPER ASSOCIATED THEREWITH, APPLYING AN AQUEOUS ALKALINE PROCESSING COMPOSITION TO SAID EXPOSED PHOTOSENSITIVE ELEMENT TO EFFECT DEVELOPMENT AND TO FORM AN IMAGEWISE DISTRIBUTION OF UNOXIDIZED DYE DEVELOPER IN UNDEVELOPED AREAS OF EACH OF SAID SILVER HALIDE EMULSIONS AS A FUNCTION OF SAID DEVELOPMENT, SAID PROCESS INCLUDING THE STEP OF TRANSFERRING BY DIFFUSION AT LEAST A PORTION OF SAID IMAGEWISE DISTRIBUTIONS OF UNOXIDIZED DYE DEVELOPER TO AN IMAGE-RECEIVING LAYER IN SUPERPOSED RELATIONSHIP THEREWITH TO THEREBY PROVIDE A MULTICOLOR DIFFUSION TRANSFER IMAGE, SAID DEVELOPMENT BEING EFFECTED IN THE PRESENCE OF A PYRAZOLO(3,4D)PYRIMIDINE OF THE FORMULA 3,6-DI(Y-),4-X-1H-PYRAZOLO(3,4-D)PYRIMIDINE WHEREIN EACH Y IS HYDROGEN OR A 1 TO 5 CARBON ALKYL GROUP AND X IS HYDROGEN, -NH2 OR -NH-R, R BEING A 1 TO 5 CARBON ALKYL GROUP OR AN ARALKYL GROUP OF 7 TO 10 CARBONS.
 2. A diffusion transfer color process as defined in claim 1 wherein said pyrazolo-(3,4d)pyrimidine is pyrazolo-(3, 4d)pyrimidine.
 3. A diffusion transfer color process as defined in claim 1 wherein said pyrazolo-(3,4d)pyrimidine is 4-aminopyrazolo-(3, 4d)pyrimidine.
 4. A diffusion transfer color process as defined in claim 1 wherein said pyrazolo-(3,4d)pyrimidine is 4-benzylamino-pyrazolo-(3,4d)pyrimidine.
 5. A diffusion transfer color process as defined in claim 1 wherein there is also present during development a 6-alkylamino purine of the formula:
 6. A diffusion transfer color process as defined in claim 5 wherein said 6-alkylamino purine is 6-benzylamino purine.
 7. A diffusion transfer color process as defined in claim 1 wherein said pyrazolo-(3,4d)pyrimidine is present in said processing composition in a concentration of about 0.1 to about 1 percent by weight of said processing composition.
 8. A diffusion transfer color process as defined in claim 1 wherein said pyrazolo-(3,4d)pyrimidine is present in said processing composition in a concentration of about 0.1 to about 0.7 percent by weight of said processing composition.
 9. A diffusion transfer color process as defined in claim 1 wherein a layer containing titanium dioxide is positioned between said image-receiving layer and said silver halide emulsions whereby said transfer image may be viewed without separating said image-receiving layer from said silver halide emulsion.
 10. A diffusion transfer color process as defined in claim 9 wherein said titanium dioxide is initially present in said processing composition.
 11. A photographic product for use in forming a diffusion transfer image in color comprising a photosensitive element comprising a support carrying a blue-sensitive silver halide emulsion having a yellow dye developer associated therewith, a green-sensitive silver halide emulsion having a magenta dye developer associated therewith, and a red-sensitive silver halide emulsion having a cyan dye developer associated therewith; a second, sheet-like element positioned in superposed or superposable relationship with said photosensitive element; an image-receiving layer positioned in one of said elements; a rupturable container releasably holding an aqueous alkaline processing composition adapted, when distributed between a pair of predetermined layers carried by said photosensitive element and said second element, to develop said silver halide emulsions and provide a diffusion transfer image in color on said image-receiving layer; said processing composition including a pyrazolo-(3,4d)pyrimidine of the formula
 12. A photographic product as defined in claim 11 wherein said pyrazolo-(3,4d)pyrimidine is pyrazolo-(3,4d)pyrimidine.
 13. A photographic product as defined in claim 11 wherein said pyrazolo-(3,4d)pyrimidine is 4-aminopyrazolo-(3,4d)pyrimidine.
 14. A photographic product as defined in claim 11 wherein said pyRazolo-(3,4d)pyrimidine is 4-benzylamino-(3,4d)pyrimidine.
 15. A photographic product as defined in claim 11 wherein said second element includes said image-receiving layer carried by a transparent support, and said processing composition includes titanium dioxide.
 16. A photographic product as defined in claim 11 wherein said pyrazolo-(3,4d)pyrimidine is present in said processing composition in a concentration of about 0.1 to about 1 percent by weight of said processing composition.
 17. A photographic product as defined in claim 11 wherein said pyrazolo-(3,4d)pyrimidine is present in said processing composition in a concentration of about 0.1 to about 0.7 percent by weight of said processing composition.
 18. A photographic product as defined in claim 11 wherein said processing composition also includes a 6-alkylamino purine of the formula
 19. A photographic product as defined in claim 18 wherein said 6-alkylamino purine is 6-benzylamino purine. 